Correct Answer - Option 4 : Luminous Efficiency
Concept:
Luminous efficiency: It is also known as radiant efficiency. It is defined as the ratio of energy radiated in the form of light, that produces a sensation of vision to the total energy radiated out by the luminous body.
Radiant efficiency = (Energy radiated in the form of light) / (Total energy radiated by the body)
It depends on the temperature of the source.
When an electric current is passed through a conductor, some heat is produced to I2R loss, which increases its temperature of the conductor. At low temperatures, the conductor radiates energy in the form of heatwaves, but at very high temperatures, radiated energy will be in the form of light as well as heatwaves.
Alternate definition
Luminous efficiency: It is defined as the ratio of the total luminous flux emitting from the source to its electrical power input in watts.
Lamp efficiency = luminous flux / power input
It is expressed in lumen/watt.
